Interface electronic structure of Ta2O5–Al2O3 alloys for Si-field-effect transistor gate dielectric applications

Abstract

Interfacial electronic structure is important for a fundamental understanding of the properties of field-effect transistor (FET) device structure systems. Previous studies using soft x-ray photoelectron spectroscopy (SXPS) have demonstrated well-defined interface states that appear at binding energies between the peaks due to the substrate Si and the oxide SiO2. Recently we have shown that significant interface changes with annealing for the SiO2/Si system commonly used for FET gate dielectrics illustrating the effectiveness of SXPS for the current study. The present article presents SXPS studies using synchrotron radiation of the electronic structure at the interface between Ta2O5–Al2O3 alloys and Si(111). This system is typical of FET alternative-gate-oxide films and has an electronic structure characteristic of high-k gate dielectrics. Thin films (<20 Å) of Ta2O5–Al2O3 alloys were carefully prepared using remote plasma enhanced chemical vapor deposition on Si(111). For this study, SXPS spectra were taken for the Si 2p, Al 2p, and Ta 4f core levels. The Si 2p SXPS data confirm that SiO2 is formed at the Si interface during deposition for all alloys (in agreement with previously published results) and that the Si interface is qualitatively similar to SiO2/Si samples. The binding energy of the Si4+ Si 2p3/2 core level varies significantly for our alloy samples and this is interpreted as a screening effect rather than being due to Ta or Al silicate formation. The Al 2p and Ta 4f SXPS core level peak positions reveal screening effects. For these data, line shape analysis also supports alloy homogeneity as independently determined by Auger electron spectroscopy and Fourier transform infrared spectroscopy.